As electric drive vehicles, such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and all-electric vehicles (EVs), produce much less noise than their internal combustion engine (ICE) vehicle counterparts, vehicle manufacturers typically install pedestrian warning systems in these vehicles, which produce sufficient noise to alert pedestrians, cyclists, and the blind to their presence during operation. Pedestrian warning systems may produce sound that mimics traditional ICE sounds, or other types of warning sounds that include pitch shifting. While these warning systems provide a useful and important service, they can be disquieting to the vehicle occupants who hear them in the vehicle's interior cabin.
In the United States, proposed government regulations specifying minimum pedestrian warning sound levels have been recently developed as part of the Federal Motor Vehicle Safety Standards (FMVSS) for electric and hybrid vehicles. In order to meet these requirements, many vehicle manufacturers may need to implement modifications to existing vehicle specifications. For example, larger speakers may be required to meet the low frequency sound level requirements of these mandated pedestrian warning systems. These modifications will likely add to the overall manufacturing costs and mass of the vehicles.
Accordingly, it is desirable to provide a means to comply with pedestrian warning system requirements while mitigating the undesirable sounds perceived in the vehicle cabin, and minimizing additional product costs.